My loop cuts are not going around my whole model
The problem is caused by the face that I've selected in the image below (I'm usin a non-default colour theme, so my selections are blue, not orange).



If that ledge really needs to be there, you should give it some volume, but if you're not going to render any views where it's visible, you may just as well delete it, and the loop cut will work.

As it is now, Blender can't tell which direction the cut should go, so it stops before actually reaching that edge.

To delete the face, select it and press X followed by F. Then the loop cut will work as you expect.
If you really need that ledge, select the face and press Y or click Mesh -> Vertices -> Split to separate it from the rest of the mesh. If so, you should also consider solidifying it, CtrlE followed by S or Mesh -> Faces -> Solidify. To set the thickness, enter it in the tool options at the bottom of the tool shelf on the left side. To show the tool shelf if it's not visible, press T or click View -> Tool Shelf.



Now the loop cut will work. However, the ledge will not be cut, since it's no longer connected to the rest of the mesh. You will need to cut it as well, if you need it to be cut at the same places as the archway.